The Australian Transport Safety Bureau (ATSB) is Australia's national transport safety investigator. The ATSB's function is to improve safety and public confidence in the aviation, marine and rail modes of transport. The ATSB is Australia's prime agency for the independent investigation of civil aviation, rail and maritime accidents, incidents and safety deficiencies.

Summary

Summary

When the SA227 Metro aircraft was turning onto the downwind leg
of the circuit, the crew noticed that the left-engine fire warning
annunciator light was illuminated. The phase-one emergency
procedures were immediately initiated. Those procedures included
immediate recall and checklist prompted actions. Accordingly, the
engine was shut down. Shortly after, the fire warning light
extinguished. The pilot in command (PIC) then decided not to
activate the fire bottle. A single-engine approach and landing was
conducted.

This was the third left-engine fire indication the aircraft had
experienced since September 1999, the previous two having occurred
over a two-week period. The PIC was involved in all three events.
During the first and second events, the fire warning indications
had remained illuminated following engine shutdown, and the PIC had
discharged the corresponding fire extinguisher into the engine fire
zone on both those occasions. However, the PIC chose not to
discharge the fire extinguisher during the most recent event as the
fire-warning indications had extinguished following the engine
shutdown. The company's chief pilot supported that decision.

Following the first event, maintenance investigation carried out
by the operator revealed that the insulation on a wire in the
fire-warning system wiring harness had chafed through while in
contact with a nearby bracket. That damage was rectified. After the
second event, the fire-detection system was checked for operation.
No fault that could have contributed to the activation of the
fire-warning system was found. Notwithstanding, it was considered
that the lower-turbine fire detector was possibly too close to the
engine, and may have resulted in a spurious fire indication. The
detector was re-positioned and the aircraft returned to
service.

Investigation of the most recent event showed that one of the
fire detectors was activating at an incorrect temperature. The
aircraft was returned to service following replacement of that
detector with one capable of activating within the correct
temperature range. At the time of writing this report, similar
problems had not re-occurred.

The phase-one emergency checks are described in detail in the
operator's aircraft flight operations manual and in the aircraft
flight manual. The immediate recall actions require that the engine
be shut down with the "stop and feather" control, and that the fuel
and hydraulic oil be isolated, before the fire extinguishing system
is discharged. The procedure is to then be continued from a written
checklist. Items identified as recall actions are intended as a
non-discretionary response to a fire warning.